Within organisms, stem cells switch between quiescence and proliferation as part of developmental programs, during adult homeostasis, and for repairing tissue after damage. Quiescence versus proliferation decisions require coordination of stem cell-intrinsic factors with extrinsic factors, local and systemic, that vary in response to changing animal physiology. Nutrient availability is an important extrinsic factor as nutrients serve as the building blocks for the macromolecular biosynthesis that drives cell growth and proliferation. Yet, it remains unclear how dietary nutrient conditions integrate with stem cell-intrinsic factors to control quiescence versus proliferation decisions. We use Drosophila as a model to determine how neuroblast proliferation decisions are made in response to dietary amino acid availability during development.

The panels above show single brain lobes from animals fed for 24 hours and then starved on 20% sucrose for the indicated number of days. The numbers of proliferating neuroblasts as measured by Edu incorporation (green) declines over time, while the overall number of neuroblasts (marked in red) remains constant. At 7 days after food withdrawal (7AFW), only the four mushroom body neuroblasts (arrows) continue to proliferate.